/Engine/Source/Editor/UnrealEd/Public/Kismet2/BlueprintEditorUtils.h
Go through the world and build a map of all actors that are referenced by other actors.
static void GetActorReferenceMap ( [UWorld](API\Runtime\Engine\Engine\UWorld) * InWorld, [TArray](API\Runtime\Core\Containers\TArray)< [UClass](API\Runtime\CoreUObject\UObject\UClass) * > & InClassesToIgnore, [TMap](API\Runtime\Core\Containers\TMap)< [AActor](API\Runtime\Engine\GameFramework\AActor) *, [TArray](API\Runtime\Core\Containers\TArray)< [AActor](API\Runtime\Engine\GameFramework\AActor) * > > & OutReferencingActors )